Speedometer "Error" on your Latio ?

[fickle]

Hi all,

noticed there is a speedometer "error" on my 2008 Latio Premium CVT.  Understand that this is common, but just curious what's the range of errors the rest are getting.

for myself, using a gps to compare

Speedo says 50km/h, GPS say 45km/h
Speedo says 70km/h, GPS say 64km/h
Speedo says 90km/h, GPS say 82km/h
Speedo says 100km/h, GPS say 92km/h

:)

[robtan99]

Hi

Trust your car, not the GPS. 

Reason is there is some latency time for the signal to reach from your GPS to the saterite as compare to the speedometer which is at the exact location.

Same theroy as ever wonder why it always take time to link the GPS to the saterite.  At least 10 mins for COLD start.

Hi all,

noticed there is a speedometer "error" on my 2008 Latio Premium CVT.  Understand that this is common, but just curious what's the range of errors the rest are getting.

for myself, using a gps to compare

Speedo says 50km/h, GPS say 45km/h
Speedo says 70km/h, GPS say 64km/h
Speedo says 90km/h, GPS say 82km/h
Speedo says 100km/h, GPS say 92km/h

:)

[lyh1280]

Yeah, GPS will be less accurate when compare with ur speedometer..

the other factor, u using stock tyre or upgrade to bigger rims/tyres?

[SoL]

Yup, bigger rims give false readings, slightly higher than normal.

[clarence]

Yup, bigger rims give false readings, slightly higher than normal.

Yes, got to watch your speedometer very carefully.

[rongshu]

GPS reading should be more accurate than the speedometer.
Take into consideration that car manufacturer most likely to show a slightly higher reading for whatever safty reason.
My GPS always shows about 5 to 10kph less.

If you are talking about the GPS signal latency, the speed of signal is almost light of speed.  The latency I'm more concern is the computing speed of the GPS device. Most GPS only update every 1 second.  But it won't matter if the car is travelling at constant speed for a while aready.

I once travelled with my FIL on NSH.
His camry shows 110kph while mine is almost 120kph.

[burnolise]

Hmmm.....then when you are carught speeding...how do u argue tat ur speedometer display a different speed from what they detect with their radar gun?

[SoL]

Police and speed cameras only catch you if you exceed speed limit by 10km/h. So cameras only take picture at 90km/h if the speed limit is 80km/h. Got some room for error lor. Best is drive at speed limit, safest!

[Jazz]

Yes, got to watch your speedometer very carefully.

Better to focus your attention on the road then the speedometer if you are driving.

[rongshu]

I just want to say that our speedometer shows a slightly higher reading.  From what my FIL said, I won't be caught speeding even if our stock latio shows 120kph on NSH.  I've sit in his car to ipoh for a few times and never caught speeding.  So depending on the speed (80-110), +5 to +10 should be fine.  the actual speed is lower.

[rongshu]

when the show your speed sign is ready, we can all test our speedometer's accuracy.

[liewks]

Same here. Speedometer reading higher than GPS. I tend to believe that GPS numbers are correct. GPS readings tend to agree with some of the radar displays that LTA has set up.

[Ying]

speed of distance/time vs displacement/time

I believe the speedo meter give us speed measured from our wheels, The GPS give corrdinate only, the "speed" it gave is derived from a calculation. Using 2 coordinate divide the time taken it gives you displacement speed at most, the division it self will some some accuracy/round off problem.  If one can spin the car, the speedo should have some reading but GPS give 0 kph.

like some bro said, pay more attention to the car and road than the speedo when driving. Driving under speed limit can kill if you always look at the meter but not the road.

[clarence]

Better to focus your attention on the road then the speedometer if you are driving.

What I meant is that we need to keep watch on our speedometer occasionally too, bearing in mind that the upgraded rim and tyre configuration will result in a faster actual speed than the speed shown on the speedometer.

And sometimes when driving downhill, you can unknowingly exceed the speed limit and get a speeding ticket.

[Jazz]

What I meant is that we need to keep watch on our speedometer occasionally too, bearing in mind that the upgraded rim and tyre configuration will result in a faster actual speed than the speed shown on the speedometer.

And sometimes when driving downhill, you can unknowingly exceed the speed limit and get a speeding ticket.

Are you sure definitely will increase in speed if change profile in rim and tyres ?

If you are a seasoned driver, you can roughly estimate the speed even if you dun see your speedo.

[LaChio]

Yup, bigger rims give false readings, slightly higher than normal.

No, bigger rim doesn't mean higher reading than normal. It depends on the profile of the tyre you use and hence, the overall circumference. For example, the overall circumference of 205/50R16 is slightly smaller than the stock 185/60R15. So for those on 205/50R16, eg. when the speedometer shows 90kmh, actual speed is less than that. In this case, the GPS reading should be more accurate if you are cruising on a (more or less) constant speed.

[SoL]

No, bigger rim doesn't mean higher reading than normal. It depends on the profile of the tyre you use and hence, the overall circumference. For example, the overall circumference of 205/50R16 is slightly smaller than the stock 185/60R15. So for those on 205/50R16, eg. when the speedometer shows 90kmh, actual speed is less than that. In this case, the GPS reading should be more accurate if you are cruising on a (more or less) constant speed.

I learned something new today! 

[fickle]

Same here. Speedometer reading higher than GPS. I tend to believe that GPS numbers are correct. GPS readings tend to agree with some of the radar displays that LTA has set up.

these days, i tend to go a lil bit faster than usual... :)  hehe

[liewks]

It is very unlikely that rounding errors in a double precision calculation would result in such a huge error. More likely, errors will be due to uncertainty in positioning.

Yes, if updates are too infrequent, then errors can result from deviations from straight line movement. But if you perform the experiment on a straight stretch of road, then such errors are miniscule and can be safely ignored.

GPS time is used to synchronise precision timebases. It is extremely accurate.

I believe the speedo meter give us speed measured from our wheels, The GPS give corrdinate only, the "speed" it gave is derived from a calculation. Using 2 coordinate divide the time taken it gives you displacement speed at most, the division it self will some some accuracy/round off problem.  If one can spin the car, the speedo should have some reading but GPS give 0 kph.

[SoL]

GPS polling time should be fast enough to account for non linear distance bah. Im not too sure on how long between calculations though.